Pyongyang: North Korean jet fighters have sortied close to South Korean airspace at least 10 times since President Lee Myung-bak took office last month, according to newspaper reports.

The news comes at a time of already heightened tensions between the two countries. On Friday, North Korea test-fired a series of short-range missiles in what analysts said was a show of anger at Washington and the new government in Seoul.

North Korea has also threatened to attack South Korean naval ships found in disputed waters, and suspend dialogue. It also threatened pre-emptive strikes to "not merely plunge everything into flames, but reduce it (the South) to ashes".

South Korean has criticised the North’s human rights record and accused the government of stalling on nuclear disarmament talks.